Undefined behavior sanitizer type/casting error

[phillip-keldenich]

Issue Details

Compiling basically any source code using CGAL::Arrangement_2 causes some errors being detected by the undefined behavior sanitizer (at least the one in my compiler); the code seems to be doing unchecked downcasts to a pointer type for which this seems to cause undefined behavior. At runtime, no actual errors occur, but since UB is a fickle source of headaches and nose demons, of course CGAL's code should not rely on this. It is, of course, possible that this may be a fault of the sanitizer itself, but since it is built into the compiler I tend to give it the benefit of the doubt right now.

Source Code

For instance, the following minimalistic example exhibits the behavior.

#include <CGAL/Arrangement_2.h>
#include <CGAL/Arr_segment_traits_2.h>
#include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
#include <iostream>

using Kernel = CGAL::Exact_predicates_inexact_constructions_kernel;
using ArrTraits = CGAL::Arr_segment_traits_2<Kernel>;
using Arrangement = CGAL::Arrangement_2<ArrTraits>;

int main() {
  Arrangement arr;
  std::cerr << "Unbounded face is unbounded: " << arr.unbounded_face()->is_unbounded() << std::endl;
  return 0;
}

The full output is:

Unbounded face is unbounded: /path/to/cgal/include/CGAL/Arrangement_2/Arrangement_2_iterators.h:293:9: runtime error: downcast of address 0x60b0000000f0 which does not point to an object of type 'value_type' (aka 'CGAL::Arrangement_on_surface_2<CGAL::Arr_segment_traits_2<CGAL::Epick>, CGAL::Arr_bounded_planar_topology_traits_2<CGAL::Arr_segment_traits_2<CGAL::Epick>, CGAL::Arr_dcel<CGAL::Arr_segment_traits_2<CGAL::Epick>>>>::Face')
0x60b0000000f0: note: object is of type 'CGAL::Arr_face<CGAL::Arr_vertex_base<CGAL::Point_2<CGAL::Epick>>, CGAL::Arr_halfedge_base<CGAL::Arr_segment_2<CGAL::Epick>>, CGAL::Arr_face_base>'
 00 00 00 00  a8 8c 9f 05 01 00 00 00  01 00 00 00 be be be be  00 01 00 00 b0 60 00 00  00 01 00 00
              ^~~~~~~~~~~~~~~~~~~~~~~
              vptr for 'CGAL::Arr_face<CGAL::Arr_vertex_base<CGAL::Point_2<CGAL::Epick>>, CGAL::Arr_halfedge_base<CGAL::Arr_segment_2<CGAL::Epick>>, CGAL::Arr_face_base>'
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /path/to/cgal/include/CGAL/Arrangement_2/Arrangement_2_iterators.h:293:9 
/path/to/cgal/include/CGAL/Arrangement_2/Arrangement_2_iterators.h:340:12: runtime error: downcast of address 0x60b0000000f0 which does not point to an object of type 'value_type' (aka 'CGAL::Arrangement_on_surface_2<CGAL::Arr_segment_traits_2<CGAL::Epick>, CGAL::Arr_bounded_planar_topology_traits_2<CGAL::Arr_segment_traits_2<CGAL::Epick>, CGAL::Arr_dcel<CGAL::Arr_segment_traits_2<CGAL::Epick>>>>::Face')
0x60b0000000f0: note: object is of type 'CGAL::Arr_face<CGAL::Arr_vertex_base<CGAL::Point_2<CGAL::Epick>>, CGAL::Arr_halfedge_base<CGAL::Arr_segment_2<CGAL::Epick>>, CGAL::Arr_face_base>'
 00 00 00 00  a8 8c 9f 05 01 00 00 00  01 00 00 00 be be be be  00 01 00 00 b0 60 00 00  00 01 00 00
              ^~~~~~~~~~~~~~~~~~~~~~~
              vptr for 'CGAL::Arr_face<CGAL::Arr_vertex_base<CGAL::Point_2<CGAL::Epick>>, CGAL::Arr_halfedge_base<CGAL::Arr_segment_2<CGAL::Epick>>, CGAL::Arr_face_base>'
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /path/to/cgal/include/CGAL/Arrangement_2/Arrangement_2_iterators.h:340:12 
1

Environment

• Operating system (Windows/Mac/Linux, 32/64 bits): MacOS
• Compiler:

Apple clang version 17.0.0 (clang-1700.0.13.5)
Target: x86_64-apple-darwin24.5.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin

• Release or debug mode: Debug with sanitizers
• Specific flags used (if any): -O0 -g -fsanitize=undefined,address -std=c++20
• CGAL version: 6.0.1
• Boost version: 1.89.0
• Other libraries versions if used (Eigen, TBB, etc.): probably not applicable

[Akifdevs]

Hey I can work on this can you assign me this issue ?